Process of making fine particle alkaline earth metal carbonates



I I I I I I-I-II- |NVENTOR3 R. R. MGCLURE ET AL Filed April 4, 19:58

PROCESS 0F MAKING FINE PARTICLE ALKALINE EARTH METAL CARBOATES I'e'f//ng Tests of 4. 75 Z Suspension 0f (a 7-.5 I I I @Il I I az's I I5i.

I I IBI Jan. 30, 1940.

0 I I I I I R. i2. MccLuRE ET AL Jan. 3o, 1940. l,

PROCESS 0F MAKING FINE PARTICLE ALKALIIU!y EARTH METAL CARONATES FiledApril 4, 1938 5 Sl'lee'lls- Sheefl 2 Serf/fhg 72'575 of 4.75% Suspensionof Ca VC03 in Wafer: 4.5 hau/5 Suspension Raymond McClure Jahn P..Seguin Gra/775 Per L fre/*pf Suc/056.

Jan. 30, 1940. R R, MCCLURE ET AL y 2,188,663

PROCESS 0F MAKING FINE PARTICLE ALKALINE EARTH METAL CARBONATES FiledApril 4, 1958 5 Sheets-Sheet 3 IAL-I I I I eff/l' INvENToRs i IIIIII -ILi L L I I 3 Grams Per L/'er ofi/arose Bag/m ond E. McClure @l I I i IJohn, I. Segum 7M 9 @M 736W; 4%.

Jan. so, 1940.

R. R. MCCLURE ET AL PROCESS OF MAKING FINE PARTICLE ALKALINE EARTH METALCARBONATES Filed April 4',"`1938 5 sheets-sheet 4 lvl 50 INVENTORSpension rec 10 J5 zo I I I.

I Ziisi lagrl? I G rams Per L #er ofj/cfose, RqymondR-McClufe v v JohnP. ,Seguin Jan. 30, 1949.

R. R. MccLLJRE E-r AI.

PROCESS OF MAKING FINE PARTIGLE ALKALINE EARTH METAL CARBONATES FiledAprfil 4, 1938 5 ,Sheets-Sheet 5 Sewing 7ss of 4.

7.5 Z Suspension of Ca C0 1.06 5.6'. Ca (0l/g ISL/5 -LII INVENTORI.)`

I T I I IWI I I; I

1 who .vISLmEmIN Grams Per L [fe/Sorb /`70/ Patented Jan. 30, 1.940`

UNITED N STATES ,PATENT ottici-1 of Delaware Application Aprr 4, .1933,-seal N01. 199,910

This invention relates generally to the production of iine particlealkaline earth metal car-y i bonates by treating a suspension oi`alkaline' earth;

metal hydroxide with carbon dioxide gas to form fine particle alkalineearth metal carbonates; The invention is applicable to the production`oi 'nne particle carbonates of calcium, barium and strontium but'W-illbe described in detail Yinconnection with the production o -calciumcarbonate.l The invention consists essentially '.in'the addition to thesuspension of calcium hydroxide in Water of one or more additionagents,y which enable the production of fine particle size calciumcarbonate of substantially colloidal 'character' Aover. a vWider rangeof temperatures, concentrationsl of calcium hydroxide and Without-therigid.

control ofother factors Which it has been necessary to take intoconsideration in carrying out..

processes according to the prior-art.y The addition agents which Weemploy for aiding'the pre-l` cipitation oi" our fine particle sizecalcium car-` bonate are the monosaccharides,A disaccharides" andpolyhydroxy alcohols containing 4, -or 6 I.

hydroxyl groups.

In the accompanying drawings,y which illustrate certain embodiments ofour invention and also an embodiment'r according to the prior art,`

the iguresvare charts showing the results obtained by settling orsedimentation tests' to 'dete'r- 'f mine 'the relative particle size ofthe calciumrcarbonate precipitated from calcium hydroxide solu-y tionsunder various conditions. f

Figure l represents the results of. tests on cal-- cium carbonate madein accordance `with the prior art, and Figures 2 through 5 representthe" results of testsmade according to the-present invention byemploying certain addition agents in the suspension of calciumyhydroxide Whichwa'sf treated Withycarbon dioxide gas.

The process 4of precipitating calcium carbonate from calcium hydroxideWater suspension" by treating the suspension" with carbon oli-oxide gaslWell known. in .this process, it'isknownfthat' factors which govern thesize oi'the particles'fo'f`- the resulting 4calcium carbonate are:v v l(l) vThe purity` of the lime used in ymaking the calcium hydroxide Watersuspension.

2) The method used for slaking the lime make the calcium hydroxideYwater suspension.

(3) The rate of addition of the carbon dioxide gas-to the calciumhydroxide Watersu'sr'zenson,I` (4) The degree of agitationAduririg'tlire'ac-f'- tion between'the carbon'dioxide gasy and the calfncium hydroxide.

V(5) The .concentration of the calcium 'hy-N twee'nthe carbon dioxideand the calcium` hy-f droxide .suspension is carried out, also thecontrol exercised to prevent undue rise in the temperay ture during thereaction.

Thetwo last mentioned factors are oimajor importance. By proper controlof all of the above mentioned factors, particularly 'concentration ofthe'calcium hydroxide. suspension and the temperature of reaction,fit isknown 'that the particle size of the calcium carbonate can be made tovary from a .substantially colloidal character to a' relatively coarseparticle size similar toa nnely pulverized ylimestone Whiting.

`In one method of making ne particle size cal,`

cium carbonate in accordance with the prior art, the reactiontemperature of the calcium hydroxide slurry, when treated with carbon`dioxide, `Was maintained at a temperature between 10 and 25 C. byemploying refrigeration.v At y temperatures below 10 C., .the particle size increased quite rapidly With decreased temperature. At temperaturesabove C.,the` particle size increased with increased temperatures, beingnollonger of substantially, colloidal character. vThus there. is averynarrow temperature range in Which-the reaction can be carried out,and itis necessary to employ cooling .apparatuain order to obtain thisrigid/temperature control. Ii cooling coils.l are employed 4for thispurpose, they tend to become coated With'calcium carbonate scale, whichacts as a. heat insulator, thereby rendering the coolto employ a calciumhydroxide suspension having a speciiic gravity of approximately 1.06. Inmore dilute slurries, the Aamount of water;v to lhandleis excessiveandin more concentrated slurries', it is diicult to maintain the necessaryvrigid temperature-.control oi 'between l0 and-'25? C.,.` because oifthelarge amount of heat given oi in the reaction'. i i i By the addition ofcertain agents tothe calcium hydroxide suspension, in accordance withthejpresent invention, and as hereinafter more) particularly described,the temperature range at which the reaction Ywith carboirdioxid'e is'carried ,outv is greatly widened, so `as to avoid the need forrefrigeratiomand indeed toivavoid the need for rigicltemparture control,and yet produce calvcium carbonate oi substantially 'colloidalcharracter;y The-addition agentsare inexpensive, may vbe readily removedby washing or if left in the.

monosaccharides, disaccharides, or the polyhy-V droxy alcoholscontaining 4, 5 or 6 hydroxyl groups. Among the monosaccharides(Cel-1120s) are glucose, fructose, galactose and mannose. Among' thedisaccharides (CizHzzOn) are sil-- Both the monosac crose, lactose andmaltose. charides and the disaccharides fallA in the gen'- eral class ofsugars. because of its availability, it is preferred to use sucrose asthe addition agent.

Among the polyhydroxy alcohols which may bev I used as addition agentsand Which contain 4, 5 or 6: hydroxyl groups maybe mentionedl erythritolC4He(OH)4,"arabitol, xylitol and adonitol, eachofthe formula C5HP1(OH)5,and mannitol, dulcitol and sorbitol, i each of the formula C6Hs(OH) 6.

-- Toillustrate the value of our invention, a large number of samples ofcalcium carbonate Were prepared by the known process, that is, bytreating suspensions of calcium hydroxide in Water With'carbon dioxidegas, and the relative particle size was determined. We then prepared alarge number of Asamples of calcium carbonate by treating With carbondioxide gas suspensions of calciumhydroxidein Water, which suspensions`also contained various quantities of addition agents of the typepreviously referred to and the `relative particle size of the Vresulting`calcium Carbonate was determined. Inall tests, a high purity calciumkoxide Was slaked in pure Waterunder. closely controlled similarconditions. .The same` source of carbon` dioxide gas was .usedin allsamples and the rate of addition of carbon dioxide vand degree ofagitation of the calcium hydroxide `suspension were uniformly controlledin the preparation ofall samples. Tests were.

carriedout usingcalcium hydroxide suspensions of different specificgravities. The temperatures of reactionfof the .calciumhydroxide slurryand carbon dioxidegaswere varied over Wide .ranges4 and the amounts ofaddition agents were also varied.. Temperature control was. `maintainedthroughout .the entire precipitation process to" plus or .minus five.tenths of one grade. The relative particle sizeof the resulting calciumcarbonate vvas determined bysettling tests carried out in the followingmannerz--A Water suspension of 25 grams of each dried sample `of calciumcarbonate or other alkaline. earth metal carbonate in five. hundredcubic centimeters of distilled Water was made by dispersing the samadegree centi;`

ple until ythe mixture Was completely homoge`` neous.This'suspensioncontained 4.75% calcium carbonate by Weight. 'I'heconditions of disper-1 sion inregard `to time, temperature and 4otherdetails of procedure were identical for allsamples.

mensionasealed and set aside for 48 hours.:` At

.f the end of this period, measurements were made to? vdetermine theheight ,of the column to which the dispersed calcium carbonate hadsettled. It I will be understood that after the settling periodthere'was a'layer vof clear supernatant liquid on' top and-al layerbelowA it containing the settled vnatant Water.

For economic reasons and Equal volumes of the dispersed samples wereplaced in clean glass tubes of -uniform fdl f calcium carbonate. Theoriginal height of the suspension was taken as 100% and the heightoflthe settled out solids Was recorded as per cent of the total height ofsolids plus clear super- The -calcium carbonates of liner particle size,

when completely dispersed .in distilled Waten' were, due to the largeamount of exposed surfaces, found to settle out only very slightly,Whereasithe calcium carbonates oflarger particle size Were,l duel to therelatively small area of exposed surface, found to settle out almost'lcompletely. In the charts, therefore, the higher vper centsrepresent thefiner particle sizes, and

the lowerk per cents the larger particle sizes.

Referring'more particularly now to Figure l,

U chart represents the results of tests made by treating calciumhydroxide in Water suspensions with carbon dioxide gas, the suspensionsnot containing any addition agents. Tests were carried out` withsuspensions having specific rgravities of 1.02, 1.03,.1.04, 1.05,- 1.06,1.07 and 1.09. At each concentration of calcium hydroxide, samples Werereacted with carbon dioxide,

thetemperatures of the slurry ranging from l` These percentages arethose rec `corded on the charts of Figuresl through 5.

C. to C., each temperature being controlled in each case to plus orminus .5 C.' In` Figure l, the specific gravities are plotted asabscissas and the temperatures at which the calcium hydroxide suspensionwas reacted with carbon dioxide gas are plotted as the ordinates.

A portion of the graph is enclosed by the line A, the areawithin theline including only sam-` ples in Which the size of the calciumcarbonate particles yWas such that the height of the settled solids, asdetermined by the settling tests, exl.

ceeds These per cents, as previously indi. cated, are usedto representthe relative iineness of the calcium carbonate particles and vvill be.referred to hereinafter as the settling factor. n It will be noted thatonly a relatively small area" is` included Within the line A, showingthat only Within very restricted conditions of temperatures of reactionand specific gravities vcan the very' fine particle sizecalciumcarbonate be obtained. It is tobe understood,v of course, thatthe present invention is not limited to the production .of

is 90 or greater, butthis factorhas been taken for comparative purposesto show the Wider variations in temperature of reaction andconcentration of calcium hydroxide in Water suspensions, x which may beemployed in accordance with the present invention, as hereinafterpointed out.

l These data `shovv that at a vspecific gravity of 1.02, particleshaving a settling factor of 90 or greater cannot be obtained at any ofthe reac tion temperatures. vThe rangesfof reaction temperatures atwhich particles having a `settling factor of f90 or greater maybe madeare indicated in thefollowing Table I for the `different specicgravities of suspension of calcium hy.y

droxide in Water:

particles of a size such that the settling factor n no casedoesthereactionl temperature range exceed 15t C.f` and `for most specificgravities, the.

rangeoftemperatureis 10. C. or less- Furthermore, the temperatures whichmustnbeemployed are all relatively 1ow,.so that refrigeration mustbeemployed. Thesedata show thatboth the concentrationy of the calciumhydroxide Vsuspension and the temperature of the reaction must beclosely f controlled to produce calcium,l -carbonate 1 ySincel thereactionv of -forming'calcium hydroxide water suspensions of thesmallest particle size.

from calcium-oxide and Water evolves vlarge quan'- tities of heat, themilkofflime'required forthe 'in water the lindicated quantities ofsucrose. The

specific gravity of the 'calcium hydroxide-sucrosewater suspensionbefore treatment with the carbon dioxide gas was 1.06. The conditions ofprecipitation of the calcium carbonatel by carbon dioxide and the methodemployedl in determining the settling-factors were the same as thoseemployedin the tes'ts'represented in Figure 1.

vBefore making the settling'tests, the precipitated samples of calciumcarbonate were ltered, l

washed substantially'free from sucrose and dried.

'Ihose samples having a settling factor of 90 or greater are locatedwithin the' area bounded 'by the line B. It will be noted that theareawithin the'A line B isl many times larger than 4thearea bounded bythe line A. From these data, it is shown that the range of reactiontemperature at which very fine particle size calcium carbonate l can beprecipitated is very vmuch extended beyond the range of reactiontemperatures' which may be employed with calcium hydroxide in watersus-` pensions butnotcontaining addition agents. The following Table IIgives the reaction temperature ranges which may be employed to' producecalcium carbonate having a particle size such that the settlingfactor is90 orv greater, when various amounts of sucrose ranging from 1/2 gramper liter to 10D grams per liter of the suspension are employed.

Grams per liter sucrose Temperature C.

o l i 2 5 1o 15 25 50 Figure 3 is a chart similar to "Figure 2, exceptthat the specic gravity ofthe calcium hydroxidef sucrose-watersuspension was 1.09-,- Here again the area-bounded by the line C'is manytimes greater than the area boundedby the line A.' Also the reactiontemperature range is increased I greatly over that which may be employedwithout the use` of an addition agent and 'stilliproduce sucrose-watersuspension was 1.03.

' in rubber, paint and other plastics.

calcium carbonate of the-same settling" factor.

The corresponding Table III shows the range of reaction temperaturesfor: the corresponding amountsof sucrose which may be employed inproducing`- calcium carbonate having a settling factor of 90 or more. 1

TABLE IIL-1.0.9 S. G. Ca( OH) z-Sucrose-water suspension y Grams per` DTemperature C. mer. sucrose Figure 4 is similar to Figures 2 and. 3,except that the specific gravity of the calcium hydroxide- I-Iere againthe temperature ranges which may be employed are considerably greaterthan those which may be employed as represented in Figure l... InFigurev 4l,

the line D designates the area including settling factors of 90 orgreater and the'corresponding data are shown in Table IV.

TABLE 1v.-1.03 s. G. caroHn-swcmsa-water suspension 4 Grams perTemperature C. liter sucrose Figure 5 represents-the kresults obtainedusingsorbitol as the addition agent, the specific gravity of the calcium`hydroxide-soibitol-vvater suspension being 1.06. This graph shows thatcalcium ycarbonate having a settling factor of 90 or greater may beobtained within the ranges of about l5 to'- The several figures showthat precipitated calcium carbonate having a iineness corresponding to asettling factor of 90 or greater may be obtained `within a widervariation of concentration of the calcium hydroxide in Water suspension,at greater temperature range variation-than.- can be used where anaddition agent is not employed, and thatwhere an addition agent such asthose described is used the naturally occurring reaction temperaturesresulting from slaking lime and carbonating the slurry may be employedWithout resorting to the use of refrigeration.

Although the invention is not restricted to vthe production of particlesizes represented vby a settling factor of 90 or greater, samplesshowing a settlingfactor of 90v or greater have been found to possess'excellent reinforcing properties showing a settling rfactor of 75,although of somewhat less value than those having a` settling factor of9i) or greater, still'have reinforcing value when used as a reinforcingpigment vfory Vrubber far 'beyond ordinary Whitingl such as a nelyground commercial'natural Whiting. For comparative purposes, a sample of-inely ground commercialk natural Whiting was vfound to lhave a settlingfactor of. l0., A,sfa1nple of' Samples y precipitated chalk ofsuperlight commercial grade had a settling factor of 37.5. Our inven-.tion is useful in-producingany of these `sizej particles but isparticularly useful in the production of particle sizes represented by asetv tling factor of or more.v

In order to produce the optimum results withr regard to particle size,it is advisable to varythe quantity of addition agent in accordance withthe concentration of the calcium hydroxide slurry. However, we havefound that the addition of sucrose, for example, to a calcium hydrox-The specific' gravity of vthe suspension to be treated with carbondioxide may be any. value from slightly over one up to, say 1.15 or1.20,

depending upon the einciency of the stirring apparatus. The specificgravity is limited only by the eiciency of the stirring apparatus, sinceany specific gravity may be employed, provided that the stirrer willagitate the slurry sufciently, when treatedA with carbon dioxide gas.The diiiiculties of emcient agitation increase materially when thespecic gravity exceeds about 1.09, due to the fact that the gel whichforms upon the addition of carbon dioxide becomes rather diicult towork. It is, therefore, preferred to employ specic gravities notexceeding 1.09, the preferred specic gravity being about 1.06.

The amount of sucrose or other addition agent may vary between 1/2 gramand 100 .grams per liter of the calcium hydroxide in water suspension,but the quantity depends upon the fineness of the particles to beproduced, the temperatures employed and the concentration of thesuspension treated with carbon dioxide. Generally the addition agentamounts to between` 1 and 50 grams per liter of the suspension andpreferably between 1 and 30 grams per liter. By reference to Figure 2,it is seen that 5 grams per liter of sucrose enables the use of anytemperature between 12 and 75 C. for the production or" calciumcarbonate having a settling fac-` tor of 90 or over.

The temperatures of reaction which may be employed may vary betweenabout 5 and 80 C. and are generally between 10 and 75 C Although theinvention has been described pare y ticularly in connection with theproduction of calcium carbonate from calcium hydroxide suspensions, itis to be understood that the other alkaline earth metals, such as bariumand strontium, may be used in place of calcium for 'the production ofthe corresponding carbonates. The

invention is not limitedto the preferred re-Y action vtemperatures,concentrations of suspen-V sion or quantities of addition agents but maybe otherwise embodied within the scope of the following claims.

We claim:

1. A process of precipitating alkaline earth metal carbonate of fineparticle size, which comprises treating with carbon dioxide a watersuspension of alkaline earth metal 'hydroxide containing a crystalline,completely water-soluble material of the class consisting ofmonosaccharides, disaccharidesf and polyhydroxy' alcohols containing 4,5 or 6 hydroxyl groups whichdo no t react with the alkaline earth metaltofform an insoluble precipitate.

2. A processor precipitating calcium carbonate."

of ne particle fsize, -which comprises treating. with carbon dioxide awater suspension of cal-f cium hydroxide containing a crystalline,completely water-soluble material of the class con.-

sisting of monosaccharides, disaccharides and;

p olyhydroxy alcohols ycontaining 4,v 5'or 6 hy-fl droxyl groupsvwhich-do not react with-the cal-l cium to form in insolubleprecipitate.y

3. A processory precipitating calcium carbonate 15 with carbon dioxide awater suspension of calof line particle size, which comprises treatingcium hydroxide` containing a crystalline, com pletely water-solublematerial of the class consisting of polyhydroxy alcohols containing/1,25

or 6 hydroxyl groupswhich do not react with the calcium to form aninsoluble precipitate.

4. A process of precipitating calcium carbonate of ne particle size,which comprises treating with carbon dioxide a water suspension of cal-4cium hydroxide of specific gravity between slightly over 1 and 1.20, andcontaining a crystalline, completely water-soluble material of theclassconsisting of monosaccharides, disacchaf rides, and polyhydroxy alcoholscontaining 4, 5 or 6 hydroxyl groups which do not reactwith the calciumto form an insoluble precipitate.

5. A process of precipitating calcium carbonate Y of fine particle size,which comprises` treating with carbon dioxide a water suspension'ofcalcium hydroxide at a temperature between about 5 C. and 80 C., thesuspensionof calcium hy droxide having a specific' gravity'betweenslightly over one and 1.20 and containingfrom 1/2 gram to grams of acrystalline, completely water-j soluble material. of the classconsisting of monosaccharides, disaccharides and 'polyhydroxy--alcoholscontaining 4, 5 or 6 hydroxyl groupswhich do not react. with the calcium`to form,

an insoluble precipitate. 6. A process of precipitating calciumcarbonate 0f ne particle size, which comprises treatin-gM with carbon`dioxide a water suspension of vcalcium hydroxide at a temperaturebetween abouty 10 C. and 75 C., the suspension of calcium hydroxidehaving a specic gravity between slightly over oneand 1.20 and containingfrom 1 gramv to 50 grams of a crystalline, completely water;

Soluble material of the class consisting of monosaccharides,disaccharides and polyhydroxy alcohols containing 4, 5 or 6-hydroxyl'groups which do not react with v ble precipitate.

7. A process of precipitating calcium. carbonatel of fine particle size,which comprises treating With carbon dioxide a water suspension ofcalcium hydroxide at a temperature` between about the'calcium to form aninsolubf C. and 75 C., the suspension. of calcium hy-v droxide having aspeoic gravity betweenvslightly f over 1 and 1.15 andcontainingfrom/about 1 to 30 grams of a crystalline, completely water-solu- 'bleAmaterial of the lclass consisting of vmono-f saccharides,disaccharidesor polyhydroxy alco-fv hols containing 4,5 or 6 hydroxylgroups which `do not react with the calcium` to form an insolubleprecipitate. n,

8. A process of precipitating calcium carbonate of fine particle size,which comprises treating with carbon dioxide a 'water suspensionofcal--V cium hydroxide at a temperature between about 5 C. and 75.l C.,the suspension ofl calcium hydroxide having a specific gravity betweenslightly over 1 and 1.15 and containing from about 1/2 gram to 100 gramsof a crystalline, completely VWater-soluble material of theclassconsisting of ypolyhydroxy alcohols containing 4, 5 or 6 hydroxylgroups which do `not react Withl thel talline, completely Water solublemonosaccharide which does not react 4with the alkaline earth metal'toform an insoluble precipitate.

10. A process of precipitating alkaline earth l metal `carbonate of neparticle size, which comprises treating-with carbon dioxide avwatersus'- pension of calcium hydroxide containing@ crystalline, completelyWater soluble 4disaccharide which does not react With the alkaline earthmetallto form an insoluble precipitate.

RAYMONDl R. MCCLURE. JOHN'PIERRE SEGUIN.

